The possible blockade of voltage-operated calcium channels (VOCs) by Andrographis paniculata dried extract in vas deferens smooth muscle was investigated in rats. The tissues were incubated in Ca(2+)-free Kreb's solution and stimulated with KCl (40 mM) to produce depolarisation of the membrane. The isometric contractile response to cumulative concentrations of CaCl(2) was effectively blockaded by 0.2 and 0.4 mg/ml A. paniculata. In other experiments, the maximum contractile response induced by norepinephrine was not antagonised by 0.2, 0.4 or 0.8 mg/ml A. paniculata. The possible blockade of Ca(2+) entry by A. paniculata was evaluated with 45Ca(2+) uptake in vas deferens treated with reserpine (5 and 2.5 mg/kg) 48 and 24 h before the experiments. Epididymal segments were incubated with Ca(2+)-free Kreb's solution with KCl, 25 and 50 mM. The influx was completely blockaded with 0.4 mg/ml A. paniculata. These results suggest that A. paniculata selectively blockades VOCs, hence inhibiting the 45Ca(2+) influx.